The present invention relates to an air jet spinning machine for producing spun threads from staple fiber strands, having a number of spinning positions, to each of which compressed air nozzles are arranged for the purpose of generating the spinning twist. The machine includes a joint compressed air regulator connected upstream of the spinning positions, the regulator including a pressure sensor and a regulating device for adjusting the measured static pressure.
An air jet spinning machine is known from German published patent application DE 38 36 481 C2, which discloses a compressed air regulator that reacts to changes in the constantly monitored spinning tension. In one variation, an attempt is made to keep the spinning tension constant in that the pressure acting on the compressed air nozzles is correspondingly adjusted. For this purpose, a pressure sensor is arranged to the compressed air regulator, which transfers the measured data to a control system for analysis. The control system includes a regulating device for changing the respective pressure.
In the case of the air jet spinning machines according to the present invention, the problem is somewhat different, as it is not provided that the pressure on hand at the compressed air nozzles is adjusted at any one time to the monitored spinning twist. Rather, a solution is sought in which the static pressure acting on the compressed air inlet of a longer air jet spinning machine is independent of how many spinning positions are operational at any one time. The operational pressure of the spinning mill, namely that which is considered to be constant, prevails at the compressed air inlet of an air jet spinning machine and measures as a rule 6 bar. If, however, all spinning positions are in operation, the static pressure can fall below 5 bar. If only a number of the spinning positions are in operation, the drop in static pressure is correspondingly lower. The latter is, for example, the case when the air jet spinning machine is starting up, or when several spinning positions are temporarily not in operation due to an end break.
It is an object of the present invention to permanently maintain a constant level of static pressure independently of how many spinning positions of an air jet spinning machine are in operation.
This object has been achieved in accordance with the present invention in that the compressed air regulator is set at a reference pressure, which corresponds to the unregulated static pressure prevailing when all the spinning positions are in operation, and in that the compressed air regulator re-adjusts to the reference pressure when a change in the static pressure occurs.
According to the invention, the compressed air regulator, which includes a compressed air sensor and a regulating device, is designed as a true actuator, by which the static pressure at the compressed air inlet of the air jet spinning machine is kept constant. If, for example, a number of spinning positions fail, resulting in an increase in the static pressure, the compressed air regulator adjusts the static pressure back down to the level of the reference pressure. When the stopped spinning positions are subsequently put into operation again, the downwardly adjusted pressure drops again, but is adjusted upwards again to the level of the reference pressure by the compressed air regulator.
The reference pressure cannot, of course, be greater than the lowest unregulated level of static pressure occurring when all the spinning positions of an air jet spinning machine are in operation. It is, however, by all means possible to choose the reference pressure at a lower level than that of the above mentioned static pressure.
In one embodiment of the present invention, it is provided that the chosen reference pressure is lower than the unregulated static pressure when all spinning positions are in operation. A lower level reference pressure is by all means possible within certain limits and has the advantage in that the static pressure can always be adjusted upwards and also downwards. This “pressure play” permits, for example, not only the static pressure to be kept constant, but also permits variations in the yarn twist within certain limits at a pre-determined draw-off speed of the spun thread.